1. Field of the Invention
The invention relates to a nuclear reactor installation arranged in the cavity of a pressure vessel, with a nuclear reactor, the core, surrounded by a thermal side shield, which is being traversed from top to bottom by a cooling gas, with a plurality of main loops, each containing within the pressure vessel a heat exchanger and a blower, together with two gas conduits to connect the said components with the reactor core, and with a plurality of auxiliary loops for the removal of decay heat, wherein each auxiliary loop is connected by means of two gas conduits with the reactor core.
In nuclear reactor installations, rapid shutdowns (insertion of absorber rods) are followed in the core by the development of decay heat, which initially amounts to approximately 4% of the nominal thermal capacity. This decay heat development declines rapidly at first and then slower and in its later variation approaches a value of zero asymptotically. In order to prevent an excessive rise in temperature in the reactor core, the decay heat must be removed from the core.
2. Description of the Prior Art
It is part of the state of the art to equip nuclear reactor installations of higher capacities with auxiliary loops for the removal of decay heat, each of which contains auxiliary heat exchangers and auxiliary blowers. The auxiliary heat exchangers are connected by means of gas conduits with the hot gas and cold gas collector spaces of the reactor. During normal operation, the auxiliary heat exchangers are closed, for example by gravity actuated butterfly valves on the auxiliary blowers, which causes a slight backflow of cold gas over the auxiliary heat exchangers. No hot gas can therefore pass by free convection in the auxiliary heat exchangers.
In high temperature reactors at least two auxiliary loops are provided for the removal of decay heat; they may be operated independently of each other and independently of the main loops. Because these systems are important from the standpoint of safety engineering, there are very high requirements concerning their operating availability and safety. In German Offenlegungsschrift No. 31 41 734 and 32 26 300, and in German P No. 33 44 527.3 high temperature reactors equipped with such auxiliary loops are described.
Every installation for the removal of decay heat comprises: (1) an intermediate cooling water loop, wherein by means of a circulating pump, water is circulated through the auxiliary heat exchangers; (2) an intermediate cooler, in which the water transfers its heat to a service cooling water loop; and (3) the auxiliary loops with the auxiliary heat exchangers and the auxiliary blowers for the cooling gas. In the intermediate cooling water loop, a further circulating pump and a cooling tower are arranged. The intermediate cooler, the circulating pumps and the service cooling water loops are located outside the reactor pressure vessel.
One disadvantage of the known decay heat removal installations is that it is composed of several active components, such as pumps. A second disadvantage is if a tube fractures in the auxiliary water exchangers, which must be anticipated, a large volume of water (up to several m.sup.3) may enter the reactor core. Furthermore, the auxiliary heat exchanger involved in no longer available for the removal of decay heat because it must be shut off as soon as possible.